title: Subsidence and nonunion after anterior cervical interbody fusion using a stand-alone polyetheretherketone (PEEK) cage.
abstract: BACKGROUND
  The purposes of the present study are to evaluate the subsidence and nonunion that occurred after anterior cervical discectomy and fusion using a stand-alone intervertebral cage and to analyze the risk factors for the complications.
  
  
  METHODS
  Thirty-eight patients (47 segments) who underwent anterior cervical fusion using a stand-alone polyetheretherketone (PEEK) cage and an autologous cancellous iliac bone graft from June 2003 to August 2008 were enrolled in this study. The anterior and posterior segmental heights and the distance from the anterior edge of the upper vertebra to the anterior margin of the cage were measured on the plain radiographs. Subsidence was defined as ≥ a 2 mm (minor) or 3 mm (major) decrease of the segmental height at the final follow-up compared to that measured at the immediate postoperative period. Nonunion was evaluated according to the instability being ≥ 2 mm in the interspinous distance on the flexion-extension lateral radiographs.
  
  
  RESULTS
  The anterior and posterior segmental heights decreased from the immediate postoperative period to the final follow-up at 1.33 ± 1.46 mm and 0.81 ± 1.27 mm, respectively. Subsidence ≥ 2 mm and 3 mm were observed in 12 segments (25.5%) and 7 segments (14.9%), respectively. Among the expected risk factors for subsidence, a smaller anteroposterior (AP) diameter (14 mm vs. 12 mm) of cages (p = 0.034; odds ratio [OR], 0.017) and larger intraoperative distraction (p = 0.041; OR, 3.988) had a significantly higher risk of subsidence. Intervertebral nonunion was observed in 7 segments (7/47, 14.9%). Compared with the union group, the nonunion group had a significantly higher ratio of two-level fusion to one-level fusions (p = 0.001).
  
  
  CONCLUSIONS
  Anterior cervical fusion using a stand-alone cage with a large AP diameter while preventing anterior intraoperative over-distraction will be helpful to prevent the subsidence of cages. Two-level cervical fusion might require more careful attention for avoiding nonunion.
authors.affiliation: Depatment of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Jae Jun
authors.initials: JJ
authors.lastname: Yang
authors.forename: Chang Hun
authors.initials: CH
authors.lastname: Yu
authors.forename: Bong-Soon
authors.initials: BS
authors.lastname: Chang
authors.forename: Jin Sup
authors.initials: JS
authors.lastname: Yeom
authors.forename: Jae Hyup
authors.initials: JH
authors.lastname: Lee
authors.forename: Choon-Ki
authors.initials: CK
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D001672:Biocompatible Materials; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D017586:Diskectomy; D005260:Female; D006801:Humans; D016268:Internal Fixators; D055959:Intervertebral Disc Degeneration / Q000601:surgery*; D007659:Ketones; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D011475:Prosthesis Failure; D011843:Radiculopathy / Q000601:surgery; D011859:Radiography; D012044:Regression Analysis; D012307:Risk Factors; D013118:Spinal Cord Diseases / Q000601:surgery; D013123:Spinal Fusion / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D001672:Biocompatible Materials; D007659:Ketones